Dual mode electrographic recorder

ABSTRACT

Dual mode electrographic recording apparatus comprising a slow speed input generated by a typewriter keyboard and a high speed input via a computer. The recording apparatus of the present invention is characterized by the provision of a developer structure having two modes of operation during one of which developer material is applied to the recording medium along a recording zone traversed by the slow speed recorder and zone occupied by a stationary high speed recording structure.

United States Patent [151 3,686,676 3 Howell et al. [451 'Aug. 22, 19724] DUAL MODE ELECTROGRAPHIC 3,570,453 1 3/1971 Nuzurn ..1 18/637RECORDER 3;283,703 11/1966 Childress.....,...'......l18/637 X n entors:s. I v- X bah 9 Webster N- Primary Examiner-Howard w. Britton [73]Assigneez' Xerox Corporation, Stamford, Attorney-James Ralabate JohnBeck and Conn. Benjamin B. Sklar [21] A 85054 Dual mode electrographicrecording apparatus comp prising a slow speed input generated by'atypewriter s2 u.s.,c1. ..346/74 ES, 101 lDlG. 13, 118/637 keyboard nhlgh Speed Input v a qm The 51 Int. Cl ..B05b 5/02, 003 15/08 rewdmgapparatus 0f the W charac- [58] Field of Search "346/74 101 /DIG terizedby the provision of a developer structure havl'l8/637 637x ing two modesof operation during one of which a I developer material is applied tothe recording 'medium p along a recording zone traversed. by the slowspeed 1 d r' g M r recorder and zone occupied by a stationary high speedUNITED STATES PATENTS r recordingsmcwre-r 3,308,473 "3/1967 :SaWazaki..1 18/637 x '9 Claims, 5 Drawing Figures [541 1' KEYBOARD COUNTER DELAY132 150 56'J -u MOTOR v 1 14 s 1 I40 144 48 STYLUS 44a HIGH sPEE 1 c1ocK MOTOR DECODER s PULSING RECORDER ESCAPEMENT 1 I 142' cmcuns HEADRELEASE E -l62 M0 1 X-CONTROL r 1 i E MOTOR 1 I e DELAY v CLUTCH MOTOR E/a4 aa L .l MOTQR [5a ca [I66 {I70 32 STYLUS HIGH sP ED DECODER PULSINGRECORDER CIRCUITS HEAD plea COMPUTER Patented Aug. 22, 1972 3Sheets-Sheet l RECORDER INVENTORS ROBERT V. BRUNNER B RICHARD S. HOWELLPatented Aug. 22, 1972 3 Sheets-Sheet 2 FIG. 3

RECORDER Fl G. 4

DUAL MODE ELECTROGRAPHIC RECORDER BACKGROUND OF THE INVENTION Thisinvention relates, in general, to a dual mode electrographic recordingapparatus and, more particularly, to a developer system for usetherewith.

Electrographic recording or the art of electrography constitutes arecording process wherein electrostatic charges are placed on aninsulating recording medium by means of electrically pulsed electrodesor styli. These electrostatic charges are rendered visible by theapplication of electroscopic marking particles by means of a brush orbrush-like structure. Subsequently exposures, of the particles adheringto the recording medium, to heat or solvent vapor renders the imagespermanent.

As is well known, the foregoing recording process is an effectivetechnique for producing alphanumeric hard copy output at high speeds aswell as at low speeds. Accordingly, one application for this process isa keyboard computer terminal wherein the recording mechanism is operatedat a relatively low speed in response to the keyboard input and at arelatively high speed in response to input from a computer;

Heretofore,'the utilization of dual recording speeds in keyboardterminals has been accomplished by the provision of different mechanicaldrive arrangements for moving a single recording structure through arecording zone. Such drive arrangements are quite complex, adding to theoverall expense of the apparatus and reducing reliability thereof.Moreover, they seriously limit the maximum recording speed obtainable.

The provision of low and high speed recording structures operating inlow and high speed recording zones, respectively, obviates theabove-mentioned shortcomings of .the prior art, particularly, in anarrangement which utilizes an incremented recording head for the lowspeed input while utilizing a fixed array of conductive styli positionedin the high speed recording zone, the latter of which eliminates therequirement for a complex drive arrangement for the high speed mode ofoperation. Movement of the low speed recording head can be accomplishedsimply and inexpensively through a stepping motor or a continuous motorin conjunction with a clutch mechanism.

In keeping with the optimum design criteria (i.e., simple construction,high speed differentials and minimum expense) with respect to the fixedand moving recording structures employed in the electrographic recordingarrangement discussed above, it is necessary to provide structure havingthe capability of and improved developer system for use in a dual modeelectrographic recorder.

BRIEF SUMMARY OF THE INVENTION Briefly, the above cited objects areaccomplished by the provision of a dual mode recorder including a dualmode developer system capable of presenting developer material to arecording medium along or in two separate spaced apart recording zonesincluding a low speed recording zone and a high speed one. The developersystem is so constructed that it uses a single supply of developermaterial. To this end, an elongated brush or brush-like structure, inone mode of operation, serves as a developer applicator for developingelectrostatic images adjacent the high speed zone and in a second modeof operation serves as a donor for a second applicator brush orbrush-like structure which develops electrostatic images on-line? in thelow speed zone.

Other advantages and features of thepresent invention may become moreapparent from reading the following detailed description in connectionwith the drawings forminga part hereof. Y

DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view of anelectrographic recording apparatus representing the invention; FIG. 2 isa fragmentary perspective view of a low speed recording structure anddrive therefor, forming a part of the apparatus of FIG. 1; I

FIG. 3 is a cross-sectional view of a modified form of a developerstructure for use in the apparatus of FIG. 1;

FIG. 4 is a view similar to that of FIG. 3, but illustrating a differentmode of operation; and

FIG. 5 is a block diagram illustrating one method of controlling theapparatus shown in FIGS. 1 and 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION anelongated web supported on a supply reel (not shown) from which it isspooled through actuation of web transporting structure generallyindicated at 14. The web transporting structure comprises a motor 16drivingly connected, as schematically illustrated, to one of a pair ofweb feed rollers 18 and 20.

The web transporting structure 16 serves to move the recording web 12through a high speed recording station 22, a first developing station24, a low speed recording station 26 and a fusing station 28. The otherdeveloping station is at the recording station 26 to thereby provideon-line" image development. A

backing electrode structure 30 supports the recording web at therecording stations as well as the developer stations and has anelongated dimension which extends perpendicular to the longitudinaldimension of the recording web.

The backing electrode 30 cooperates with the high speed electrographicrecording structure 32, stationarily supported at the recording station22. The recording structure 32 has an elongated dimension which issubstantially coextensive with the backing electrode to formtherebetween a high speed recording zone. The recording structurecomprises a stylus arrangement 34 which in the preferred mode osoperation contacts the recording web 12, however, the styli constitutingthe array may be spaced from the web 12. The specific details of thearray which are not shown may comprise a linear configuration, extendingin the direction of the elongated dimension, of parallel styli orconductive electrodes which are electrically insulated one from theother.

The recording structure 32 is commonly employed for the generation ofalphanumeric characters at very high speeds. With such a structure eachcharacter or symbol is composed of selected areas from a matrix ofareas. For example, a plurality of 5 X 7 matrices may be employed, onefor each alphanumeric character to be recorded by ,the recordingstructure along the width of the recording medium. The input to thefixed recording structure is derived from a computer and suitableinterfacing logic components. Depending upon the specific resultsdesired, the input may be serialor parallel. Other recording techniquescan be employed for example, various types of optical charactergenerators could be substituted for the electrographic system described,the primary requisite being in the speed with which the characters areto be generated.

The electrostatic images placed on the recording web 12 are renderedvisible at the developer station 24 through the application ofelectroscopic marking particles 35. The foregoing is accomplished bymeans of an applicator brush or brush-like structure 36 supported forrotation by a drive arrangement including a motor 38. In the embodimentillustrated in FIG. 1, the structure 36 comprises an applying member 42having a generally cylindrical applying surface 40 mounted on a supportmember 44 which, in turn, is affixed to a shaft 46. The brush orbrush-like structure 36 is rotated such that the applying member 42moves through the marking particles 35 contained in the sump area of adeveloper supply housing or hopper 48. The marking particles ordeveloper adhere to the applying member and are therefore carriedthereby to the surface of the recording medium.

The drive arrangement and motor 38 are adapted for continuously rotatingthe structure 36 in the counterclockwise direction, as viewed in FIG. 1,during the high speed recording mode of operation. During a low speedrecording mode, the drive arrangement rotates the structure 36 in thecounterclockwise direction, in a manner to be described hereinafter.

A recording structure 48 pivotally affixed to a carriage assembly 49supported for reciprocating movement at the low speed recording station26 and through a low speed recording zone extending transversely of therecording web. A shaft 50 (FIGS. 1 and 2) supports the carriage assemblyfor such movement which is effected by a suitable motor 52 which aspresently contemplates is a continuous drive motor, however, aconventional stepping motor may be employed. The output of the motor isselectively coupled to a drive pulley 54 by a clutch not shown in detailwhich is selectively engaged or disengaged by appropriate signals. Theorigin of these signals will be discussed in detail hereinafter.

The drive pulley 54 frictionally engages a cable 56 which is supportedby idler pulleys 58 and 60. The cable 56 is attached to opposite sidesof the carriage to thereby transmit the output torque from the motor 52thereto. A carriage return mechanism (not shown) which may be aconventional clock motor is wound by the motor 52 during a recordingcycle. Unwinding of the clock motor serves to return the recordingstructure to a start-of-recording position after each recording cycle.

The recording structure 48 comprises a stylus array 62 which is notshown in detail but may include'a linear configuration of parallelconductive electrodes or styli suitably insulated electrically one fromanother. The array may be mounted in or on an insulative support forminga part of the recording structure through which electrical-conductorsmay be provided to supply electrical recording signals individually toeach stylus. These electrical conductors may terminate at any suitableplace on the recording structure in the form of a socket or other typeof electrical terminal to facilitate connection to or commutation with asource of recording signals. g

In operation the recording structure 48 is driven from left to right, asviewed fromthe right in FIG. 1 or from the upper right of FIG, 2, acrossthe recording medium 12 during the application of suitable recordingsignals to the styli. During the stepwise movement, in a manner to bediscussed hereinafter, of the recording structure a predetermined amountreferred to as a character space, a character is recorded on theelectrographic recordingmedium 12 in the form of a latent electrostaticcharge pattern. The recording medium preferably remains stationary inthe recording zone during the left-to-right traversal of the recordingstructure, during which an entire line of characters is recorded. At theterminal point of movement of the recording structure a suitablemicroswitch or other means may be actuated by the presence of therecording structure to actuate the aforementioned clutch associated withmotor 52 to disengage the pulley 54 from the motor. The clock motorpreviously referred to may then unwind expending its stored energy tomove the recording structure from right-to-left, to return it to itsinitial left margin position. The actuation of the switch which effectsthe carriage return may also be utilized appropriately for advancing therecording medium through energization of the motor 16.

A developer applicator 64 is provided for developing the latentelectrostatic images formed by the stylus array 62. The applicatorstructure 64 is supported for rotation by a shaft 66 supported insuitable bearings (not shown), the motive power being supplied by amotor 68. As shown in FIG. 2, the applicator structure 64 comprises asemicircular applying member 70 mounted on a support 72 which, in turn,is supported by the shaft 66. The applying member 70 is shown to have acylindrical developing periphery 74. A substantially planar surface 75forms an acute angle with the stylus array 62, as viewed in FIG. 1, tothereby permit instant viewability of developed alphanumeric symbols.

The developing surface 74-is loaded with electroscopic marking particles35 through contactwith the brush-like structure 36 which in the lowspeed recording mode serves as a donor structure for the applicator 64.To this end, the drive arrangement and motor 38 is adapted toincrementally rotate the brush-like structure 36, approximately 90 eachtime the recording structure 48 completes a line of recordedinformation.

The shaft 66 is provided with a key-way 76 which cooperates with aspline 78 of the applicator 64 to provide a driving connectiontherebetween. The support 72 and the carriage assembly 49 are providedwith bores for receiving the shaft 66 thereby permitting slidingmovement relative'to the shaft. To this end, the keyway 76 iscoextensive with the shaft 66.

In operation, it is preferred that the applicator 64 be advanced throughits developing cycle each time a character-shaped charge pattern isplaced on the recording medium 12. In accordance with the foregoing, themotor 68 may either be a conventional stepping motor or'it may be acontinuously running motor which is associated with a clutch arrangementwhich provides for incremental rotation of the brush.

During the high speed mode of operation the applicator 64 is rotatedapproximately 90 counterclockwise, as viewed in FIG. 1, so that it isout of contact with the recording web 12. Simultaneously, the stylusarray which now occupies the left hand margin is retracted from the web.These functions may be simply perfected by employment ofsuitable'controls for effecting momentary operation of the motor 68 tothereby rotate the applicator the required amount. The system, it willbe appreciated, may be programmed to enable the clock motor mentionedhereinabove at any time the printer is in communication with thecomputer rather thanthe keyboard. This will effect movement of thecarriage assembly 49 to its home position where a simple camarrangement, now shown, in opposition to a bias member 80 is effectiveto retract the stylus array 62 from the recording web. During the restof the high speed mode of operation the motor 68 will be inactivated.

As shown in FIGS. 3 and 4, a modified form of the developing systememployed in the embodiment of FIG. 1, is generally indicated by thereference character 100. The development system 100, like the systemillustrated in FIG. '1, is a dual mode development arrangementcomprising a development member 102 which extends across the full widthof web 12.

The development member 102 comprises a cylindrical drum member 104 theouter periphery of which may be coated with a layer 106 of polystyrenemethyl methacrylate. This substance has a strong affinity forelectroscopic marking particles and due to the rotating action of themember 102 through a supply of developer 108 comprising maskingparticles mixed with iron filings the layer becomes heavily coated withthese marking particles. Rotation of the member 102 is accomplished bymeans of a'drive arrangement including a reversible motor 110. Duringoperation of the motor 110 such as to rotate the member 102 in thecounterclockwise direction as viewed in FIG. 3, the member 102 acts as adonor for a semicircular brush structure 112 which may be similar to thebrush or applicator structure 64. During counterclockwise rotation ofthe member l02,the low speed recording mode of operation takes place.

During the high speed recording mode of operation when the printer isunder the control of a computer, the motor 110 rotates the member 102 inthe clockwise direction. Simultaneously, as in the case-of theembodiment disclosed in FIG. 1, the brush 112 is rendered inoperative inorder to prevent double development. A.

magnet 114 stationarily disposed internally of the member 102 convertsthe development system 100 to a magnetic brush system during the highspeed mode of operation with the member 102 rotating in the clockwisedirection.

The iron particles or filings attract the electroscopic markingparticles thereto and serve as a carrier therefor during the high speedoperation of the system. The magnet 114, as shown in FIG. 4, causes abrushlike orientation of the marking particles and iron filings to whichthe particles adhere about the surface of the member 102 to therebycause marking particles to be presented to the recording web atarecording zone 116. While the magnet 114 has the effect of forming arotation of the member 102, it will be seen-from a consideration of thethe field properties of the magnet 102 that during counterclockwiserotation of the member 102, the electroscopic marking and iron filingswill be confined thereby to the bottom of the trough 120.

Having described the mechanical structure of the recorder and itsdevelopment system, one possible way of controlling the modes ofoperation thereof will now be described in conjunction with the blockdiagram illustrated in FIG. 5. As can be seen the input to the highspeed recorder head 32 is derived from a computer while the input to thelow speed recorder head is derived from a keyboard 132 forming a part ofa computer terminal control 134. The tenninal is adapted to be operatedin the computer-input mode by a program control switch 136 and in thekeyboard-input mode via a program control switch 138.

The keyboard 132 may generate an appropriate binarycode uniquelyidentifying the alphanumeric symbol corresponding to the actuated key ofthe keyboard. This binary code, such as used in the American StandardCode for Information Interchange, is provided to the input of aconventional decoder circuit 140 which decodes the binary code togenerate a character pulse on one of a series of parallel outputsindicative of the alphanumeric symbol selected at the keyboard 132.Output conductor 142 is intended to represent a number of outputs, eachcorresponding to aseparate alphanumeric character of the symbolsincorporated in the keyboard 132.

' a when their respective character select wire is energized. Anotherform which the pulsing circuits may take is a magnetic core matrix,having five columns and seven rows, wherein a particular characterselect wire associated with one of the outputs 142 intertwines anappropriate pattern of magnetic cores corresponding to the alphanumericsymbol to be recorded. The pulsing circuit as well as the other parts ofthe block diagram of FIG. are not intended toform a particular part ofthe present invention per se and, therefore, are shown schematicallyonly since well known conventional circuits may be employed to providetheir functions.

Output 146 from the decoder simply provides a signal indicative of thefact that a binary codehas been decoded by the decoder 140. In thismanner, for each character entered at the keyboard 132 which effects adecoding process in the decoder 140, an output signal is generated onthe conductor 146. This effectively provides a control pulse or signalto the pulsing circuitry which may initiate, for example, in the caseofa magnetic core matrix, a distributor circuit which would sequentiallyread out each column of the core matrix at a rate correlated to thespeed of the recorder head 48. As each column is sampled by thedistributor circuit, a group of parallel outputs would be energizeddepending on the cores set by the character select wire. The

signals on these paralleloutputs would be supplied to a suitable driverstage which would provide parallel recording signals to the styli in thestylus array 62 via output 148.

Additionally, the signals present on the output 146 are supplied to aconventional counter circuit 150 via conductor 152. The counter circuit150 is used to indicate at its output 154 when a predetermined number ofcharacters have been decoded by the decoder 140. In a conventionalarrangement wherein each recorded line on the recording web 12 willaccommodate 80 characters, the capability of the counter 150 would besuch as to provide an output pulse at the output 154 when a count of 80has been arrived at by the counter medium 12. This signal is employed toeffect momentary energization from the motor 38 via conductor 158 toeffect rotation of the brush-like structure 36 through an angle ofapproximately 90 counterclockwise, as viewed in FIG. 1. The utilizationof the counter 150 and the delay device 156 is intended as exemplaryonly, of one manner for timely actuation of the brush-like structure 36at the end of each recording traversal. This may also be accomplished byapplying a microswitch, actuatable by the presence of the carriageassembly 49 at the right margin of the recording medium. The actuationof such a switch may be utilized to momentarily energize the motor 38.

Simultaneously with the energization of the motor 38 via conductor 158,an escapement release mechanism gized at this time to effect incrementalmovement of the web 12.

During a low speed recording cycle, the output pulses from the decoderserve to pulse the motor 52 via conductor 162 and delay circuit 164. Themotor 52 through its associated clutch causes movement of the stylusarray the equivalent of one character space, only after the provideddelay. The delay serves the purpose of allowing an adequate time for thestylus to place a symbol on the recording web before the stylus ismoved.

A delayed output from the decoder 140 is also utilized to pulse themotor 68 an amount sufficient to effect rotation of the developerapplicator 64. Since in the direction of recording, the applicator 64trails the stylus array 62, development of an alphanumeric character isaccomplished'during movement of the stylus array to its next recordingzone. In this mode of operation the brush 36 acts as a donor for thebrush 64.

In the computer-input or high speed mode of operation the switch 136 ofthe terminal 134 is closed thereby enabling communication with thecomputer 130 in lieuof the keyboard. In this instance, binary codedsignals from the computer are decoded by means of a decoder 166receiving such signals from the computer via conductor 168. Where theinput to the decoder 166 is a character at a time, the decoder andstylus pulsing circuitry 170 associated therewith may be the same asthat utilized in conjunction with low speed recording. Where, however,itmay be desired to simultaneously form all the characters to beprinted, other conventional apparatus may be employed.

In order to develop a line of alphanumeric characters at a time, duringthe high speed mode of operation, the drive arrangement and motor 38 iscontinuously rotated and is appropriately energized by conductor 172. Atthis time the motor 68, either directly or in-' directly through asuitable clutch arrangement, is momentarily energized to move the brush64 to its inoperative position where it is out of contact with therecording web 12.

We claim:

1'. Apparatus for rendering latent imagesvisible, said apparatuscomprising:

a first developer applicator having an arcuate surface capabie ofretaining developer, said first applicator being rotatably supportedadjacent the path of movement of a recording member;

a second developer applicator capable of retaining developer, saidsecond developerapplicator being rotatably supported adjacent the pathof movement of said recording web;

means containing a supply of developer through which said secondapplicator is rotatable;

means rendering said second developer applicator operable in a firstmode of operation to bring developer to a zone through which saidrecording member passes;

means for preventing said second applicator from bringing developer tosaid zone, in a second mode of operation; and

means operable to effect cooperative engagement of said first and secondapplicators during said second mode of operation whereby said secondapplicator serves as a donor for said first applicator.

2. Apparatus according to claim 1 wherein, said developer compriseselectroscopic marking particles mixed with iron particles; and

said means rendering said second developer applicator operable in afirst mode comprises means for rendering said second applicator operableas a magnetic brush.

3. Apparatus according to claim 2 wherein,

said means rendering said second developer applicator operable in saidfirst mode comprises drive means for rotating said second applicator inone direction; and

a magnet positioned adjacent the path of said recording web and disposedinternally of said second applicator structure, said magnet beingineffective to render said second applicator operable as a mag neticbrush during rotation of said second applicae tor in a directionopposite said one direction.

4. Combination donor and developer applicator structure for use in adeveloping system, said structure comprising: I

a member having a continuous surface, said surface exhibitingarelatively high affinity for electroscopic marking particles therebyrendering said structure suitable as a donor member; means supportingsaid member for movement in two directions; and t means for renderingsaid structure operable as a magnetic brush during movement in only oneof 3 said directions whereby said structure functions'as a developerapplicator.

5. Combination donor and developer applicator structure for use in adeveloping system, said structure comprising: i

a member having a continuous surface exhibiting a relatively highaffinity for electroscopic marking particles;

means for selectively moving said member in opposite directions; I

means for rendering said member operable as a magnetic brush duringmovement of said member in only one direction.

6. Structure according to claim 5 wherein, said.

means for selectively rendering saidmember operable as a magnetic brushcomprises a magnet stationarily disposed within said continuous surfacedmember.

7. A dual mode electrographic apparatus comprising: a linear array ofconductive styli;

an elongated backing electrode defining a first recording station; meansfor selectively incrementing said linear array ad lon ted backnelectrode and second] be twe en s ai d elongate daaacking electrode andsaifi incrementally movable array of styli;

second development applicator means positioned along the path of the webbetween the first and second recording zones having a surface capable ofretaining developer particles and rotatable about an axis parallel tothe axis of said first developing applicator means;

means rendering said second developer applicator operable in said firstmode of operation to bring developer to said web at said first recordingzone; I

'- means for preventing said second applicator from bringing developerto said web at said second recordingzone, in a second mode of operation,

while serving as a donor for said first applicator; v

and means operable to effectcooperative engagement of said first andsecond applicators Y during said second mode of operation whereby saidsecond applicator serves as a donor for said first applicator,

8. Apparatus according to claim 7 wherein,,said

developer comprises electroscopic marking particles mixed with ironfilings; and

said means rendering said second applicator operable in said first modeof operation comprises means for selectively rendering said secondapplicator operable as a magnetic brush.

9. Apparatus according to claim 8 wherein,

said means rendering said second developer applicator operable in saidfirst mode comprises drive means for rotating said second applicator inone direction and p a magnet positioned adjacent the path of movement ofsaid recording-web and disposed internally of said second applicatorstructure.

1. Apparatus for rendering latent images visible, said apparatuscomprising: a first developer applicator having an arcuate surfacecapable of retaining developer, said first applicator being rotatablysupported adjacent the path of movement of a recording member; a seconddeveloper applicator capable of retaining developer, said seconddeveloper applicator being rotatably supported adjacent the path ofmovement of said recording web; means containing a supply of developerthrough which said second applicator is rotatable; means rendering saidsecond developer applicator operable in a first mode of operation tobring developer to a zone through which said recording member passes;means for preventing said second applicator from bringing developer tosaid zone, in a second mode of operation; and means operable to effectcooperative engagement of said first and second applicators during saidsecond mode of operation whereby said second applicator serves as adonor for said first applicator.
 2. Apparatus according to claim 1wherein, said developer comprises electroscopic marking particles mixedwith iron particles; and said means rendering said second developerapplicator operable in a first mode comprises means for rendering saidsecond applicator operable as a magnetic brush.
 3. Apparatus accordingto claim 2 wherein, said means rendering said second developerapplicator operable in said first mode comprises drive means forrotating said second applicator in one direction; and a magnetpositioned adjacent the path of said recording web and disposedinternally of said second applicator structure, said magnet beingineffective to render said second applicator operable as a magneticbrush during rotation of said second applicator in a direction opPositesaid one direction.
 4. Combination donor and developer applicatorstructure for use in a developing system, said structure comprising: amember having a continuous surface, said surface exhibiting a relativelyhigh affinity for electroscopic marking particles thereby rendering saidstructure suitable as a donor member; means supporting said member formovement in two directions; and means for rendering said structureoperable as a magnetic brush during movement in only one of saiddirections whereby said structure functions as a developer applicator.5. Combination donor and developer applicator structure for use in adeveloping system, said structure comprising: a member having acontinuous surface exhibiting a relatively high affinity forelectroscopic marking particles; means for selectively moving saidmember in opposite directions; means for rendering said member operableas a magnetic brush during movement of said member in only onedirection.
 6. Structure according to claim 5 wherein, said means forselectively rendering said member operable as a magnetic brush comprisesa magnet stationarily disposed within said continuous surfaced member.7. A dual mode electrographic apparatus comprising: a linear array ofconductive styli; an elongated backing electrode defining a firstrecording station; means for selectively incrementing said linear arrayof styli through a first recording zone opposite said backing electrodeduring a first recording mode; first developer applicator means havingan arcuate surface capable of retaining developer particles for bringingsaid particles to said first recording zone, said applicator beingselectively rotatable about an axis substantially parallel to said firstrecording zone; a fixed linear array of conductive styli positionedopposite said elongated backing electrode and substantially coextensivetherewith and forming a second recording zone therebetween; means formoving a web of insulative recording medium, first between said fixedarray of styli and said elongated backing electrode and secondly betweensaid elongated backing electrode and said incrementally movable array ofstyli; second development applicator means positioned along the path ofthe web between the first and second recording zones having a surfacecapable of retaining developer particles and rotatable about an axisparallel to the axis of said first developing applicator means; meansrendering said second developer applicator operable in said first modeof operation to bring developer to said web at said first recordingzone; means for preventing said second applicator from bringingdeveloper to said web at said second recording zone, in a second mode ofoperation, while serving as a donor for said first applicator; and meansoperable to effect cooperative engagement of said first and secondapplicators during said second mode of operation whereby said secondapplicator serves as a donor for said first applicator.
 8. Apparatusaccording to claim 7 wherein, said developer comprises electroscopicmarking particles mixed with iron filings; and said means rendering saidsecond applicator operable in said first mode of operation comprisesmeans for selectively rendering said second applicator operable as amagnetic brush.
 9. Apparatus according to claim 8 wherein, said meansrendering said second developer applicator operable in said first modecomprises drive means for rotating said second applicator in onedirection and a magnet positioned adjacent the path of movement of saidrecording web and disposed internally of said second applicatorstructure.